The production of polyesters and copolyesters of dicarboxylic acids and aliphatic glycols has been carried out commercially for many decades. Among the earliest disclosures relating to this technology is the disclosure in U.S. Pat. No. 2,465,319, issued Mar. 22, 1949. Since this disclosure many variations have been made in the process and many catalysts have been discovered and patented. On Dec. 8, 1970, there issued U.S. Pat. No. 3,546,179 which is directed to the use of compounds containing both the silicon and phosphorus atoms in the molecule as catalysts.